1. Technical Field
The invention relates to vibration damping devices which develop damping performance when being applied to a suspension member, such as for automobiles or other equipment. More particularly, the invention relates to such a damping device using an electrorheological fluid as the damping medium, which device has a shorter axial height than prior similar damping devices, without sacrificing stroke length, and in which the length of the electrode plate for the electrorheological fluid is independent of stroke length.
2. Background Information
Vibration damping devices have been used for a considerable period of time to dampen the vibrational forces applied to the suspension system of vehicles to provide a smoother ride, by reducing the vibrations caused by road bumps and depressions, passing from the tires to the vehicle frame, by the interposing of oil filled shock absorbers or high pressure gas damping devices.
Although these prior art oil and high pressure gas damping devices have proven satisfactory, a more recent development has evolved in which an electrorheological or electroviscous liquid is used within the chambers of the damping device, wherein the liquid is in contact with one or more electrode plates usually mounted in a restrictive passage, which depending upon the size of the electrodes and the amount of voltage applied to the liquid, will change its viscosity, enabling the damping device to have a greater range of damping characteristics than those achieved by the high pressure gas or oil filled shock absorbers.
U.S. Pat. No. 4,973,031 discloses an anti-vibration apparatus which uses an expandable liquid chamber containing an electrorheological fluid in the chamber.
U.S. Pat. No. 4,858,733 discloses another damping device using electrode plates in combination with an electroviscous liquid contained within closed chambers and movable through a restricted passage, where voltage is applied to the electroviscous liquid as it moves through the passage to change its viscosity to achieve various damping effects.
Pending United States patent application Ser. No. 570,659, assigned to the Assignee of the present invention, discloses another vibration damping device of the type shown in FIG. 12 of the present application drawings. This damper uses an electrorheological fluid which passes between two closed chambers formed by elastomeric sleeves, through a restricted orifice, where the fluid comes into contact with electrodes mounted in the restrictive passage. This damping device is believed to be the closest known prior art to the device of the present invention.
Although the damping device as shown in FIG. 12, is satisfactory for many applications, the height thereof is approximately five times the stroke length of the movable piston therein. It is desirable for certain applications to provide such a damping device having a shorter axial length without sacrificing stroke length, due to the limited space provided in many vehicles for the mounting of the suspension system.
Furthermore, in prior art damping devices using an electrorheological fluid, the length of the orifice and electrodes in contact therewith, is determined by and dependent upon, the length of the stroke of the damping device. This limits the versatility and characteristics desired to be achieved by the damping device for certain applications.
Thus, the need exists for an improved damping device which has a shorter axial length than that of similar damping devices without shortening of the stroke length, and when used with an electrorheological fluid, enables the length of the restrictive orifice and electrode plates to be varied independent of the stroke length not believed possible with prior art damping devices.